Mastitis can be defined as inflammation of the mammary glands and is caused by a variety of microbial infections. Ordinarily, but not necessarily, bovine mastitis reflects the presence of pathogenic bacteria in the milk compartment of the udder. Two of the commonest bacteria associated with this disease are Staphylococcus aureus and Streptococcus agalactiae which are contagious and live on or in the cow's udder. Other species of bacteria involved in the disease are found in the environment of the cows.
Bovine mastitis causes more financial loss to the dairy industry than any other disease. Approximately 70% of this loss is attributed to reduced milk production caused by sub-clinical mastitis, which dairy producers seldom recognize. In addition to the loss of milk production, manufacturers of dairy products also lose money because of the adverse processing qualities of mastitic milk due to compositional changes. The major effect of the altered milk composition, particularly the lower caesin and fat levels, is a lower cheese yield.
There are several tests in use to detect mastitis infections, including milk somatic cell counts and tests based on various compositional changes in the milk. The use of somatic cell counts to diagnose udder disease was the first widely used screening procedure, and even today has retained its position as the most reliable and specific test for mastitis diagnosis. Increased levels of somatic cells can be detected by a variety of direct and indirect methods. As milk somatic cell numbers can be influenced by factors other than inflammation, for example, stage of lactation, number of lactations, stress, nutritional problems, etc., such tests are not very specific. Furthermore, this type of testing is cumbersome, in many cases expensive and not suitable for use at the cow-side.
One of the most dramatic changes seen in mastitic milk over normal milk is the ratio of lymphocytes:neutrophils:epithelial cells. In normal milk this ratio is 1:1.5:14. In mastitic milk this ratio is significantly raised, for example, 1:10:10. This increase in neutrophils is apparently specific for mastitis, and a rapid immunodiagnostic test for the quantitation of bovine neutrophils in milk would be of considerable benefit in the diagnosis and control of this condition. Furthermore, due to E.E.C. directives, in 1989 milk with 500,000 somatic cells per ml will not be acceptable and in 1990 this number will be 400,000. A specific test which would quantify neutrophils would indicate to the farmer animals with sub-clinical mastitis. Such animals could be treated with appropriate antibiotics which would circumvent milk losses.
Monoclonal antibodies have been developed to neutrophils in bovine blood and have been used to identify subpopulations therein (M. J. Paape et al. Journal of Diary Science, Vol. 71, Supplement 1, 1988 p. 258). A monoclonal antibody has also been developed to identify bovine neutrophils in milk (Lostrie-Trussart et al; Annales de Medicine Vetinaire, Vol. 131, No. 1, 1987, p. 49). A further series of monoclonal antibodies to bovine neutrophils, not thoroughly characterised have been produced, and were proposed as a means of examining the nature and number of antibody binding sites on neutrophils of bovine blood and milk as a method of distinguishing between these cells, and for use in identification of neutrophil subpopulations important to mastitis resistance (Nickerson et al. Journal of Dairy Science, Vol. 66, No. 7, 1983, p. 1547). However, none of these three references describes or proposes the use of such monoclonal antibodies in a diagnostic assay for mastitis. This is not unexpected because it has not heretofore been appreciated that neutrophil-like cells are the important cells to monitor in mastitis. It has now been found and as hereinafter demonstrated that when a milk sample has greater than 250,000 somatic cells/ml, the cells in excess of 250,000 are almost entirely made up of neutrophils
It is an object of the present invention to provide an assay for the detection of mastitis, including sub-clinical mastitis, caused by any aetiologic agent, which overcomes the aforementioned disadvantages and which can be readily carried out by farmers and veterinarians in addition to laboratory personnel.